jabey, if you could give us some more specific information we could give you more specific answers.
What muzzle velocity are you looking for for the two loads? What does the rifle weigh with scope and rings? If you don't have a scale you can weigh it on, what model rifle and scope? Is this for hunting and, if so, what kind of game at what distances? This last would help with overall recommendations.
Since the powder mass is ejected out of the barrel with the bullet the amount of recoil is a function of the total weight of the bullet and powder at a specific velocity. Felt recoil is that energy factored into the weight of the rifle, rings, scope and anything else firmly attached to the rifle. Sling weight usually doesn't count. Velocity
My experience has been that most folks loading VLDs push them pretty hard. Since the principal advantage of IMR 7828SSC is to get more powder into a case I'll guess that's what you are doing.
If you are doing that then there will be very little recoil reduction going to the lighter bullet. Since your loads would have it going faster than the 168 the recoil, for practical purposes will be close to the same. A 168 grain bullet with 54 grains of powder at 2700 FPS from an 8 pound rifle/scope combination generates 19.8 pounds of recoil force which is near the level where most shooter performance drops off due to recoil. Changing to a 140 grain bullet with 59 grains of powder at 2900 FPS the recoil is about 18.5 pounds. The recoil issue will be greatly aggravated with a very light rifle.
Most shooters, especially those who are recoil conscious, are not going to perceive the change as significant.
Again, knowing what your target is and at what ranges would help.
There is a good article on understanding recoil at:
http://www.chuckhawks.com/rifle_recoil.htmIf you are interested in developing a reduced recoil load the most versatile powder I know of is Hodgdon's H4895. You can take the maximum powder charge for any cartridge for which Hodgon lists an H4895 load and multiply it by 0.6 to come up with the lowest recommended powder charge that will uniformly ignite and give consistent pressures and velocities. If you can't find H4895 data for a particular bullet and cartridge call their tech folks. The have oodles od load data that is not on the website.
There is an article on reduced recoil loads at:
http://www.chuckhawks.com/reduced_recoil_H4895.htmHodgdon's website lists a number of reduced recoil "youth" loads as examples. All will keep the bullet inside 3" of the crosshairs out to 200 yards or more and were developed with white tail deer in mind.
Good luck
Lance